Formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO 2 reduction.

Synthesis of carbon nanostructures at room temperature and under atmospheric pressure is challenging but it can provide significant impact on the development of many future advanced technologies. Here, the formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO 2 reduction reactions (CO 2 RR) are demonstrated. Under a ternary electrolyte system containing [BMIm] + [BF 4 ] - , propylene carbonate, and water, a mixture of sp 2 /sp 3 carbon allotropes were grown on the facets of Ag nanocrystals as building blocks. We show that (i) upon sufficient energy supplied by an electric field, (ii) the presence of negatively charged nascent Ag clusters, and (iii) as a function of how far the C-C coupling reaction of CO 2 RR (10-390 min) has advanced, the growth of nanostructured carbon can be divided into three stages: Stage 1: sp 3 -rich carbon and diamond seed formation; stage 2: diamond growth and diamond-graphite transformation; and stage 3: amorphous carbon formation. The conversion of CO 2 and high selectivity for the solid carbon products (>95%) were maintained during the full CO 2 RR reaction length of 390 min. The results enable further design of the room-temperature production of nanostructured carbon allotropes and/or the corresponding metal-composites by a viable negative CO 2 emission technology.